The present invention relates to a method for manufacturing a capacitor having a ferroelectric thin-film, and more particularly, to a method for manufacturing a ferroelectric thin-film capacitor, which is used as a memory cell of a ferroelectric random access memory (FRAM).
A ferroelectric capacitor comprises upper and lower electrodes having good conductivity for transferring a charge and a ferroelectric thin-film disposed between the electrodes. In a capacitor having a ferroelectric thin-film, a lower electrode is first formed on a substrate, and then the ferroelectric thin-film is coated thereon. Thereafter, an upper electrode is formed on the resultant structure and then processed as a predetermined pattern. For processing the upper electrode, a mask is formed on the upper electrode through a photolithography process and then a part of the electrode, which is not covered with the mask, is etched. As the etching method, there are wet etching, ion beam etching, reactive ion etching, reactive ion beam etching, etc. However, in the case of the ion beam etching, the reactive ion etching or the reactive ion beam etching, ions come to be concentrated in the upper electrode, the underlying ferroelectric thin-film and/or the interfaces thereof, to thereby cause a charging phenomenon in which a coercive current increases.
Generally, the reactive ion etching method is used for processing the ferroelectric thin-film and the ion beam etching method in which the electrode is physically processed using inert gas is used for processing the electrode. In the ion etching method, an etching rate is slow due to a low plasma density and the capacitor is damaged by the physical impact of the ions and the charging effect thereof. On the other hand, in the reactive ion etching method which is widely used for processing the ferroelectric thin-film, a metal mask should be applied since the etching rate is slow in this case and a selectivity with respect to a photoresist which is mainly used as a mask is very low. Therefore, a new etching method in which a very high etching rate and high selectivity are provided is required for processing the ferroelectric thin-film and electrode.